1. Field of the Invention
This invention relates to improvements in the handleability of impact modifier polymers of the type which are used to modify polyvinyl chloride (PVC) and other polymers.
2. Description of the Prior Art
Graft polymer impact modifiers are generally used in hard polymers such as PVC, styrene resins, styrene acrylonitrile (SAN) and methylmethacrylate (MMA) resins. These graft polymers are typically prepared through emulsion polymerization of butadiene, butadiene and styrene, lower alkyl esters of acrylic acid, isoprene, and the like, to form an elastomeric polymer onto which is grafted a hard polymer, typically one or more of the following: methyl methacrylate, styrene, and acrylonitrile. When the graft polymer impact modifiers are isolated by coagulation with an acid or a salt and then dehydrated and dried to obtain a powder, especially when the impact modifier has high elastomer levels, it often agglomerates during storage and can clog or block transportation lines. This is generally referred to as a flowability problem. One solution to this problem has been proposed in U.K. patent application No. 2,044,779 published Oct. 22, 1980. The U.K. Patent teaches blending 0.1 to 25 parts of a graft polymer comprising 5 to 49% of an elastomeric trunk polymer and 95 to 51% of a branch polymer of a hard resin producing monomer grafted on the elastomeric trunk polymer to improve the powder flow and compaction properties of graft polymer impact modifiers. According to the British patent, Comparison Example 3, it is very important that the additive polymer be a graft containing an elastomeric trunk polymer, because when the hard resin polymer was tried without elastomeric trunk polymer, it caused the impact modifier polymer to possess notably poor ability to impart impact strength to PVC, and the PVC resin compositions obtained therefrom had numerous fish eyes, i.e., the modifier had a dispersability problem in PVC.